The buffer is divided into 4 words (32 bits each), named as A, B, C, and D.

Word A is initialized to: 0x67452301.

Word B is initialized to: 0xEFCDAB89.

Word C is initialized to: 0x98BADCFE.

Word D is initialized to: 0x10325476.

Step 4. Processing Message in 512-bit Blocks. This is the main step of MD 5 algorithm, which
loops through the padded and appended message in blocks of 512 bits each. For each input block,
4 rounds of operations are performed with 16 operations in each round. This step can be
described in the following pseudo code slightly modified from the RFC 1321's version: